Objective lens holding apparatus

ABSTRACT

An objective lens holding apparatus includes an upper supporting portion and a bottom supporting portion not parallel with each other. The upper supporting portion and the bottom supporting portion have respectively one end connecting to an objective lens holder and another end connecting to a supporting arm anchor dock. The objective lens is mounted to the objective lens holder and is prevented from incurring an inclined angle while the objective lens is yawing. The elastic supporting arm anchor dock can keep the high resonant frequency within a desired range to enhance the stability of the optical pick-up head during reading and writing operations.

FIELD OF THE INVENTION

The invention relates to an objective lens holding apparatus andparticularly to an objective lens holding apparatus adopted for use onoptical pick-up heads of optical reading devices (such as CD-ROM,DVD-ROM and the like) to ensure that the objective lenses move stabilityin the tracking and focusing direction to accomplish tracking andfocusing servo operations.

BACKGROUND OF THE INVENTION

Using laser beams (such as semiconductor lasers) to pick up records onoptical media (such as CDs or DVDs) is a technique known in the art. Thelaser beam is focused on the track located on the surface of the opticaldisk by means of an objective lens in the optical pick-up head. A photodetector converts the return light reflected from the optical disk intoregenerated signals to obtain the data recorded on the optical disk.During data pick-up processes, tracking signals and focusing signalsmust be obtained from the return lights, and based on these signals thetracking actuator and the focusing actuator may be controlled to movethe objective lens and ensure that the laser beam focuses correctly onthe desired track on the surface of the optical disk.

In order to accomplish the servo operations of tracking and focusing,the objective lens must be able to move freely in the optical axisdirection (i.e. the focusing direction) and the radial direction of theoptical disk (i.e. the tracking direction). Hence a special holdingapparatus for supporting the objective lens is required to providestability movement. The known holding apparatus for supporting theobjective lens can be classified as follows:

1. Wire-supporting type: U.S. Pat. Nos. 5,381,273, 5,555,623 and5,587,845 disclose this type of technique in which the objective lens issupported by four elastic metallic wires (such as stainless steelwires). The metallic wires are parallel to one another. One end of thewires is fixed while the other end of the wires connects to a lensholder. The objective lens holder and the objective lens may be moved intwo different directions under the driving of a tracking actuator and afocusing actuator to accomplish the servo operations. However, such adesign tends to produce twisting on the metallic wires during the servooperations of tracking and focusing. As a result, tracking and focusingoperations are prone to error.

2. Objective lens holder employing leaf spring: U.S. Pat. No. 5,892,628discloses such a technique. It utilizes four parallel leaf springs tosupport the objective lens. U.S. Pat. No. 5,453,881 also discloses atechnique that uses two parallel springs, an upper leaf spring and lowerleaf spring, to support the objective lens. Both of these techniques aredifficult to produce and assemble.

3. Axial sliding and rotating type device: U.S. Pat. No. 5,587,845discloses such a technique. In the FIG. 1 of this patent, the objectivelens holding device includes a supporting shaft for holding an objectivelens holder and an objective lens. The objective lens holder and theobjective lens may slide axially along the supporting shaft under thedriving of the tracking actuator and the focusing actuator, or swingabout the axis of the supporting shaft to accomplish the servooperations of tracking and focusing. However such a design requiresprecise matching dimensions for the objective lens holder and thesupporting shaft. Thus it increases manufacturing difficulty.Furthermore, in the event that the supporting shaft and objective lensholder do not match properly, the objective lens holder tends to wobble.

In addition, employing the objective lens holders set forth above, theobjective lens incurs variations of an inclined angle on the tangentline of the track while the pick-up head reads the optical disk. As aresult, reading effectiveness is adversely impacted. Therefore, there isa need to develop an improved objective lens holder to remedy thedisadvantage of variation of the inclined angle and to increase readingeffectiveness.

SUMMARY OF THE INVENTION

The primary object of the invention is to provide an objective lensholding apparatus to prevent the objective lens from incurring aninclined angle during yawing when the optical pick-up head reads/writesthe optical disk, and to keep the high resonant frequency within adesired range to enhance the stability of the optical pick-up headduring reading and writing operations.

The objective lens holding apparatus of the invention is for supportingthe objective lens of the optical system in an optical pick-up head. Theapparatus includes an objective lens holder, a supporting arm anchordock, an upper supporting portion and a bottom supporting portion. Theobjective lens holder is used to support the objective lens. Thesupporting arm anchor dock is elastic and remains stationary relative tothe optical axis of the objective lens. The upper supporting portion andthe bottom supporting portion correspond to each other and are elastic.One end of the supporting portions connects to the objective lens holderand the other end connects to the supporting arm anchor dock. The twosupporting portions may be extended to cross with each other at alocation beyond the supporting arm anchor dock.

As the non-parallel and elastic supporting portions form an inclinedangle with the supporting arm anchor dock in opposite directions, duringthe reading operation on the optical disk the inclined angles offseteach other. As a result, the objective lens is prevented from incurringan inclined angle during yawing when the optical pick-up head reads theoptical disk. Moreover, the elastic supporting arm anchor dock candampen the high resonant frequency to enhance the stability of theoptical pick-up head during read/write operations.

The foregoing, as well as additional objects, features and advantages ofthe invention will be more readily apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of the invention.

FIG. 1B is a side view of the invention.

FIG. 2 is a schematic view of the objective lens holding apparatus ofthe invention in six degrees of freedom.

FIG. 3 is a schematic view of an optical pick-up head while reading anoptical disk, with two parallel upper and bottom supporting portionsincurring an inclined angle for the objective lens during yawing.

FIG. 4 is a schematic view of an optical pick-up head while reading anoptical disk, with the non-elastic supporting arm anchor dock incurringan inclined angle for the objective lens during yawing.

FIG. 5 is a schematic view of an optical pick-up head of the inventionwhile reading an optical disk, with non-parallel upper and bottomsupporting portions and the elastic supporting arm anchor dock,resulting in no inclined angle for the objective lens during yawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1A, 1B and 2, the objective lens holding apparatus ofthe invention aims at holding an objective lens 50 in the optical systemof an optical pick-up head. The apparatus includes an objective lensholder 10, a supporting arm anchor dock 20, an upper supporting portion30 and a bottom supporting portion 40.

The objective lens holder 10 has an access hole 11 to hold the objectivelens 50, which can focus laser beams on the data recording surface of anoptical disk. The objective lens holder 10 and the objective lens 50 maybe moved in the tracking direction (TD), which is the radial directionof the optical disk, and in the focusing direction (FD), which is theoptical axis direction of the laser beams or of the objective lens 50.

The supporting arm anchor dock 20 is elastic and remains stationaryrelative to the optical axis of the objective lens. The supporting armanchor dock 20 has a base seat 21 and an elastic element 22, which is athin plate located on one side of the base seat 21.

The upper supporting portion 30 and the bottom supporting portion 40correspond to each other and are elastic. One end of the supportingportions connects to the objective lens holder 10 and the other endconnects to the supporting arm anchor dock 20. The two supportingportions 30 and 40 may be extended to cross with each other at alocation beyond the supporting arm anchor dock 20.

The upper supporting portion 30 includes a first supporting arm 31 and asecond supporting arm 32 that are parallel with each other. The firstand the second supporting arm 31 and 32 have one end connecting to theobjective lens holder 10 and the other end connecting to the elasticelement 22 of the supporting arm anchor dock 20. The bottom supportingportion 40 has a third supporting arm 41 and a fourth supporting arm 42parallel with each other. The third and the fourth supporting arm 41 and42 also have one end connecting to the objective lens holder 10 and theother end connecting to the elastic element 22 of the supporting armanchor dock 20. The first supporting arm 31 corresponds to the thirdsupporting arm 41, and the second supporting arm 32 corresponds to thefourth supporting arm 42. Each pair of the corresponding supporting armsmay be extended to cross with each other at a location beyond thesupporting arm anchor dock 20. For instance, the first supporting arm 31may cross with the third supporting arm 41 after extension, and thesecond supporting arm 32 may cross with the fourth supporting arm 42after extension.

Referring to FIG. 3, in the event that two supporting arms 30′ and 40′are parallel, when the optical pick-up head reads the optical disk, theobjective lens 50 moves with the up and down movement of the opticaldisk. The supporting arm anchor dock 20 provides a push and pull forcein the direction of the upper and the bottom supporting arm 30′ and 40′.As a result, a pitching motion is incurred to cause the objective lensto generate an inclined angle during yawing. As the supporting armanchor dock 20 is elastic, the supporting arm anchor dock 20 can dampenthe high resonant frequency.

Referring to FIG. 4, in the event that the supporting arm anchor dock20′ is not elastic, when the optical pick-up head reads the opticaldisk, the objective lens 50 moves with the up and down motion of thedisk, and the objective lens generates an inclined angle during yawing.

Referring to FIG. 5, as the two supporting arms 30 and 40 of theinvention are not parallel with each other, and the supporting armanchor dock 20 is elastic, the two opposite inclined angles offset eachother while the objective lens is yawing. As a result, the objectivelens does not incur an inclined angle. Moreover, the upper and thebottom supporting portions 30 and 40, and the supporting arm anchor dock20, can reduce the inclined angle that might incur on the objective lens50 at a low frequency motion. The supporting arm anchor dock 20 can alsokeep the high resonant frequency.

Thus, when the objective lens 50 focuses at a low frequency, theobjective lens holding apparatus of the optical pick-up head maintainsthe vibration mode in the focusing direction and enables the opticalpick-up head to move only in the FD when operating at a low frequency.Meanwhile, the rigidity in the rolling direction of the objective lenssuspending apparatus may also increase. When the objective lens 50focuses at a high frequency, the objective lens holding apparatus of theoptical pick-up head can reduce the high resonant frequency and preventresonance on other elements. Thus damping becomes fully effective toprevent harmful resonance from occurring in the high frequency zone.

By means of the objective lens holding apparatus set forth above, thefollowing results can be accomplished:

1. The invention provides non-parallel upper and bottom supportingportions and an elastic supporting arm anchor dock, and can prevent theobjective lens from incurring an inclined angle.

2. The elastic supporting arm anchor dock can keep the high resonantfrequency within a desired range without generating resonance on otherelements. Harmful resonance can be prevented from occurring in the highresonant frequency zone, and the stability of the optical pick-up headduring reading and writing is enhanced.

While the preferred embodiment of the invention has been set forth forthe purpose of disclosure, modifications of the disclosed embodiment ofthe invention as well as other embodiments thereof may occur to thoseskilled in the art. Accordingly, the appended claims are intended tocover all embodiments which do not depart from the spirit and scope ofthe invention.

What is claimed is:
 1. An objective lens holding apparatus for holdingan objective lens of an optical system of an optical pick-up head,comprising: an objective lens holder having an access hole for holdingthe objective lens; an elastic supporting arm anchor dock beingstationary relative to a vertical focusing direction; and an elasticupper supporting portion and an elastic lower supporting portion,relative to the vertical focusing direction and corresponding to eachother and having respectively one end connected to the objective lensholder and another end connected to the elastic supporting arm anchordock, the upper supporting portion and the lower supporting portionbeing extendable to cross with each other at a locating beyond theelastic supporting arm anchor dock, wherein the upper supporting portionand the lower supporting portion have respectively a plurality ofparallel supporting arms, each of the supporting arms of the uppersupporting portion corresponding to one of the supporting arms of thelower supporting portion and the corresponding supporting arms of theupper supporting and the lower supporting portion being extendable tocross with each other at a location beyond the elastic supporting armanchor dock, and the supporting arm anchor dock including a base seatand an elastic element, the elastic element being located on the baseseat on one side and connected to the upper and the lower supportingportion on the opposite side of the elastic element.
 2. The objectivelens holding apparatus of claim 1, wherein the elastic element is a thinplate.